workflows: adopting azure/setup-kubectl

There are workflows that rely on `az aks install-cli` to get kubectl
installed. There is a well-known problem on install-cli, related with
API usage rate limit, that has recently caused the command to fail
quite often.

This is replacing install-cli with the azure/setup-kubectl github
action which has no such as rate limit problem.

While here, removed the install_cli() function from gha-run-k8s-common.sh
so avoid developers using it by mistake in the future.

Fixes #11463
Signed-off-by: Wainer dos Santos Moschetta <wainersm@redhat.com>

tests/gha-run-k8s-common.sh

@@ -135,10 +135,6 @@ function install_bats() {
 	sudo add-apt-repository --remove 'deb http://archive.ubuntu.com/ubuntu/ noble universe'
 }
 
-function install_kubectl() {
-	sudo az aks install-cli
-}
-
 # Install the kustomize tool in /usr/local/bin if it doesn't exist on
 # the system yet.
 #